Pseudocumene recovery



nited States Patent 2,929,856 PSEUDOCUMENE RECOVERY Francis T.Wadsworth, Dickinson,

American Oil Company, tion of Texas Tex., assignor to The Texas City,Tex., a corpora- No Drawing. Application December 27, 1957 Serial No.705,496

4 Claims. (Cl. 260-674) This invention relates to the recovery ofpseudocumene from hydrocarbon fractions, and particularly concerns aprocess whereby pseudocumene can be produced in high concentration.

Pseudocumene is a desirable intermediate in the chemical industry forconversion to alcohols, carboxylic acids, and for a number of otherpurposes. The plastics industry is appreciating the merits oftri-carboxylic aromatic acids to a greater extent than heretofore, and anecessity for prodvcing high purity pseudocumene has arisen. Thesynthesis of pseudocumene (1,2,4-trimethylbenzene) is too costly to bepractical. Petroleum refiners have quantities of hydrocarbon fractionscontaining pseudocumene, but these fractions contain large amounts ofother trimethylbenzenes, ethyltoluenes, butylbenzenes, propyltoluenes,ethylxylenes, and propylbenzenes. These contaminating aromatics arepresent as a mixture of all of their isomers. Because of the closenessof the boiling points of other aromatic hydrocarbons, it is not possibleto separate pseudocumene fraction containing more than 70-80%pseudocumene by fractionation of petroleum naphthas. A method forproducing pseudocumene in higher concentration is desired.

An object of the present invention is to provide a process for producinga hydrocarbon fraction containing a high concentration of pseudocumenefrom an initial hydrocarbon fraction containing a lower concentration ofpseudocumene. Another object is to provide a process by whichpseudocumene is recovered from reformed naphtha fractions. A furtherobject is to provide a process by which pseudocumene in a purity of 95%and higher is produced. These and other objects will be apparent fromthe detailed description of the invention.

In accordance with the present invention a pseudocumene-rich fraction ofhydrocarbons, substantially all of which boil within the range of 164 to170 C., is subjected to an alkylation step in which an alkylating agenthaving a tertiary carbon atom, e.g. tertiary olefin such asdiisobutylene, is used. A petroleum naphtha which has been catalyticallyreformed to convert naphthenes to aromatics may be fractionated toproduce the pseudocumene-rich charge stock to this invention. Reformednaphtha charge stock to the invention may be treated by processes suchas solvent extraction to remove essentially all of the paraffinichydrocarbons prior to using the defined boiling range charge stock inthe alkylation step. An alkylation catalyst (eg; BF monohydrate ishighly effective in this process), is used. The products from thealkylation step are processed to separate the alkylation catalyst fromthe mixture of alkylated and non-alkylated hydrocarbons. Thehydrocarbons are then fractionated to separate a fraction boilingapproximately within the range of 164 to 170 C. from a higher boilinghydrocarbon fraction. The 164 to 170 C. fraction contains a higherconcentration of pseudocumene than does the initial charge stock to thealkylation step. Ninety-five percent purity pseudocumene can be producedwhen starting with a reformed naphtha fraction essentially free ofnon-aromatic hydrocarbons.

While others have heretofore employed the technique of alkylating amixture of hydrocarbons selectively so that only certain C aromaticisomers in the mixture are alkylated and thereafter separating alkylatedfrom nonalkylated aromatic hydrocarbons, there has been no suggestionthat pseudocumene could be recovered by such a technique. Also, the useof this technique in earlier processes did not produce one aromaticisomer in the high purity of which is needed in subsequent chemicalprocessing steps. The presentinvention is capable of producing 95%purity pseudocumene provided the charge stock is carefully fractionatedand is essentially free of non-aromatic hydrocarbons, e.g. paraffins andolefins.

The charge stock to this invention can be a petroleum naphtha which hasbeen reformed, preferably to an octane number of at least F-l, andthereafter fractionated to recover a pseudocumene-rich fraction,substantially all of which boils within the range of 164 to C. Prior torecovering the 164-170 C. fraction from reformed naphtha, the reformednaphtha may be freed of parafiins and olefins by solvent extraction orextractive distillation or the like. If desired, the separation ofnon-aromatic hydrocarbons from the aromatic hydrocarbons can be madeupon the 164-170 C. fraction. By using naphtha which has been reformedto an octane number of at least 100 F-l, the solvent extraction step maybe eliminated since only a very small percentage of non-aromatichydrocarbons will be present in the 164-170 C. boiling range fraction ofthe reformed naphtha. The pseudocumene-rich fraction from such a highoctane reformed naphtha is a particularly advantageous charge stock tothis invention. The 164- 170 C. pseudocumene-rich fraction which isessentially free of non-aromatic hydrocarbons will ordinarily have apseudocumene'content of about 70-80% by Weight. It may contain from 1 to5% by Weight of mesitylene, depending upon the preciseness offractionation. The other aromatic hydrocarbons consist of butylbenzene,ethyltoluenes, sometimes propylbenzenes, methylpropylbenzenes, anddimethylethylbenzenes, in their various isomeric forms.

The alkylating agent is one which has a tertiary carbon atom. It may bea tertiary olefin such as isobutylene, diisobutylene, triisobutylene, orthe like; a poly-tertiaryalkylbenzene such as a di-tertiarybutylbenzene;a tertiary alcohol; or a tertiary-alkyl halide such as tertiary-butylchloride, etc. Tertiary olefins are particularly useful for thispurpose. The process can be made quite eflicient by recycling thedi-tertiary-alkyl aromatics which are produced during the alkylationstep as a source of the tertiary alkylating agent.

The alkylation reaction may be carried out at atemperature between 0 C.to 100 C., although somewhat lower or higher temperaturesv may be used,depending upon the particular alkylation catalyst employed. Variousacidic catalysts such as have heretofore been used in aromaticalkylation may be employed. These in clude sulfuric acid, phosphoricacid, hydrofluoric acid, Friedel-Crafts catalyst such as aluminumchloride, boron fluoride, and the like. A boron trifiuoride monohydratecatalyst, which consists of approximately (not necessarily usingreaction times of from 5 minutes to 2 hours or longer.

After completion of the reaction. the catalyst is separated from thehydrocarbons. The hydrocarbons are then fractionated to'recover a164-170 C. pseudocumene fraction which has a higher concentration ofpseudcu- 'mcne than the initial charge stock. If non-aromatichydrocarbons were present in the 164170 C. pseudocumene fraction whichwas alkylated, such hydrocarbons may be removed at this point, ifdesired, by solvent extraction, extractive distillation or similartechniques.

-T he portion of the hydrocarbons from the alkylation step which boilsabove 170 C. consists of alkylated aromatic hydrocarbons.

If a high ratio of alkylating agent to non-pseudocumene aromatichydrocarbons is employed during the alkylation step, a considerablequantity of dialkylation products may be formed. These di-alkylatedaromatic hydrocarbons can be recovered and used as the source of thealkylating agent during subsequent drogen while using a platinum-aluminacatalyst, was

obtained. The reformed naphtha was subjected to highly efficientfractionation and a fraction boiling over the range of 164-169" C. wascollected. Due to the very high octane number of the reformed naphtha,this 164- 169 C. fraction contained only about of non-aromatichydrocarbons which were principally paraffins. Four hundred and eightygrams of this 164-169" C. reformate fraction, which contained .95 molsof aromatic hydrocarbons other than pseudocumene, were agitated with 2mols of diisobutylene in the presence of 150 grams of BF mono-hydrate at25 C. for about 30 minutes. Following the allgylation reaction, theaqueous catalyst phase was separated and the hydrocarbon layer waswater-washed and then dried. The dried hydrocarbon layer was thendistilled using a ten-tray Oldershaw column at IOU/reflux and a fractionboiling over the range of 164-169 C. was collected. A portion of theinitial pseudocumene-rich charge stock was also redistilled under theseidentical conditions. The analysis of the l64l69 C. fraction which hadbeen recovered from the products of alkylation, and the analysis of the164- 169 C. fraction which had not been subjected to alkylation arepresented in Table I. These analyses are presented on a paraflin-freebasis.

TABLE I Composition of 164-169 C. fraction, wt. percent Pseudo-Mesltylem Other curriece Aromatics Reco ered from Products 01'. PercentPrrcznt Percent Alkylntion 95.3 3.5 1.? Charge to Alkylation- 77. 5 3. 71s 8 It is evident from the above data that the present inventionprovides a method for recovering pseudocumene in high purity fromhydrocarbon fractions such as reformed petroleum naphthasi Thus havingdescribed the invention, what is claimed is:

1. A process which comprises contacting in the liquid phase apseudocumene-rich hydrocarbon fraction, which is essentially free ofnon-aromatic hydrocarbons and boils within the range of 164 to 170 C.,with diisobutylene in the amount of at least one mol per mol of thearomatic hydrocarbons other than pseudocumene which are present in thecharge pseudocumene-rich fraction and with a B1 mono-hydrate alkylationcatalyst at a temperature between about 0 and 100 C. and therebyproducing a mixture of alkylated and non-alkylated aromatichydrocarbons, separating the catalyst from the mixture of alkylated andnon-alkylated hydrocarbons, and fractionally distilling the mixture ofalkylated and non-alkylated hydrocarbons to separate a pseudocumenefraction which boils within the range of 164 to 170 C. and whichcontains pseudocumene in a concentration of at least from a higherboiling alkylated aromatic hydrocarbon fraction.

2. A process which comprises contacting a pseudocumene-rich fraction ofhydrocarbons, substantially all of which boils within the range of 164to 170 C., with an alkylation catalyst and an alkylating agent having atertiary carbon atom under alkylation conditions whereby a portion ofthe hydrocarbons contained in the pseudocumene-rich fraction isalkylated, and distilling products from the alkylation step to separatea non-alkylated fraction enriched in pseudocurnene and boilingapproximately within the range of 164 to 170 C. from a higher boilingalkylated hydrocarbon fraction.

3. The process of claim 2 wherein the alkylating agent is isobutylene.

4. A process which comprises reforming a petroleum naphtha to an octanenumber of at least F-l clear, fractionating the reform naphtha torecover a pseudocumeme-rich fraction substantially all of which boilswithin the range of 164 to C., contacting said pseudocumene-richfraction with an alkyiation catalyst and an alkylating agent having atertiary carbon atom under alkylation conditions whereby a portion ofthe hydrocarbons contained in the pseudocumene-rich fraction isalkylated, and distilling products from the alkylation step to separatea non-alkylated fraction enriched in pseudocumene and boilingapproximately within the range of 164 to 170 C. from a higher boilingalkylated fraction.

References Cited in the file of this patent UNITED STATES PATENTS

1. A PROCESS WHICH COMPRISES CONTACTING IN THE LIQUID PHASE APSEUDOCUMENE-RICH HYDROCARBON FRACTION, WHICH IS ESSENTIALLY FREE OFNON-AROMATIC HYDROCARBONS AND BOILS WITHIN THE RANGE OF 164* TO 170*C.,WITH DIISOBUTYLENE IN THE AMOUNT OF AT LEAST ONE MOL PER MOL OF THEAROMATIC HYDROCARBONS OTHER THAN PSEUDOCUMENE WHICH ARE PRESENT IN THECHARGE PSEUDOCUMENE-RICH FRACTION AND WITH A BF3 MONO-HYDRATE ALKYLATIONCATALYST AT A TEMPERATURE BETWEEN ABOUT 0* AND 100*C. AND THEREBYPRODUCING A MIXTURE OF ALKYLATED AND NON-ALKYLATED AROMATICHYDROCARBONS, SEPARATING THE CATALYST FROM THE MICTURE OF ALKYLATED ANDNON-ALKYLATED AROAND FRACTIONALLY DISTILLING THE MIXTURE OF ALKYLATEDAND NON-ALKYLATED HYDROCARBONS TO SEPARATE A PSEUDOCUMENE FRACTION WHICHBOILS WITHIN THE RANGE OF 164* TO 170* C. AND WHICH CONTAINSPSEUDOCUMENE IN A CONCENTRATION OF AT LEAST 95% FROM A HIGHER BOILINGALKYLATED AROMATIC HYDROCARBON FRACTION.